Target-less approach of vibration measurement with virtual points constructed with cross ratios

Abstract

For structures with distinguished edge features, a target-less approach of vibration measurement method based on stereo vision system is proposed in this paper. The edge is precisely identified through skeleton thinning, and then the virtual points are constructed and tracked. A sub-pixel algorithm to minimize continuous curvature change is used, which is based on the interpolation in the normal direction of the line edge skeleton. Virtual points are constructed according to different cross ratios. Based on the invariance of cross ratio in affine transformation, the image coordinates of the same virtual point can be found accurately. The edge displacement is measured through matching and tracking of these virtual homologous points. A 3 KW wind turbine blade is experimented. The measured frequencies are compared with those from target approach and hammer impact testing. The reliability and efficiency of the proposed target-less approach is verified by the experimental results.